Referrer spoofing

In HTTP networking, typically on the World Wide Web, referer spoofing (based on a canonised misspelling of "referrer") sends incorrect referer information in an HTTP request in order to prevent a website from obtaining accurate data on the identity of the web page previously visited by the user.

Referer spoofing is typically done for data privacy reasons, in testing, or in order to request information (without genuine authority) which some web servers may only supply in response to requests with specific HTTP referers.

To improve their privacy, individual browser users may replace accurate referer data with inaccurate data, though many simply suppress their browser's sending of any referer data. Sending no referrer information is not technically spoofing, though sometimes also described as such.

In software, systems and networks testing, and sometimes penetration testing, referer spoofing is often just part of a larger procedure of transmitting both accurate and inaccurate and both expected and unexpected input to the HTTPD system being tested and observing the results.

While many web sites are configured to gather referer information and serve different content depending on the referer information obtained, exclusively relying on HTTP referer information for authentication and authorization purposes is not a genuine computer security measure. HTTP referer information is freely alterable and interceptable, and is not a password, though some poorly configured systems treat it as such.

...
Wikipedia